The majority of present day integrated circuits (ICs) are implemented by using a plurality of interconnected field effect transistors (FETs), also called metal oxide semiconductor field effect transistors (MOSFETs), or simply MOS transistors. An MOS transistor includes a gate electrode as a control electrode and spaced apart source and drain electrodes between which a current can flow. A control voltage applied to the gate electrode controls the flow of current through a channel between the source and drain electrodes.
The gain of an MOS transistor, usually defined by the transconductance (gm), is proportional to the mobility of the majority carrier in the transistor channel. The current carrying capability and hence the performance of an MOS transistor is proportional to the mobility of the majority carrier in the channel. The mobility of holes, the majority carrier in a P-channel MOS (PMOS) transistor, can be increased by imparting a uniaxial compressive longitudinal strain to the channel. It is well known that a compressive longitudinal strain can be imparted to a silicon MOS transistor by embedding a material such as silicon germanium (SiGe) at the ends of the transistor channel. The mobility of electrons, the majority carrier in an N-channel MOS (NMOS) transistor, however, is decreased by such a compressive longitudinal strain imparted to the channel. The mobility of electrons in the channel of an NMOS transistor can be increased, however, by imparting a uniaxial tensile strain to the channel of the NMOS transistor.
Accordingly, it is desirable to provide NMOS devices having enhanced channel electron mobility. In addition, it is desirable to provide a method for fabricating a mobility enhanced NMOS device. Still further, it is desirable to provide compatible enhanced mobility NMOS and PMOS devices and methods for their fabrication. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.